The present invention relates to planarizing solutions, planarizing machines and methods for planarizing microelectronic-device substrate assemblies using mechanical and/or chemical-mechanical planarization processes.
Mechanical and chemical-mechanical planarizing processes (collectively xe2x80x9cCMPxe2x80x9d) are used in the manufacturing of microelectronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate assembly 12. The planarizing machine 10 has a support table 14 with a top panel 16 at a workstation where an operative portion (A) of a polishing pad 40 is positioned. The top panel 16 is generally a rigid plate to provide a flat, solid surface to support the operative section of the polishing pad 40 during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the polishing pad 40 over the top panel 16. The rollers include a supply roller 20, first and second idler rollers 21a and 21b, first and second guide rollers 22a and 22b, and a take-up roller 23. The supply roller 20 carries an unused or preoperative portion of the polishing pad 40, and the take-up roller 23 carries a used or post-operative portion of the polishing pad 40. Additionally, the first idler roller 21a and the first guide roller 22a stretch the polishing pad 40 over the top panel 16 to hold the polishing pad 40 stationary during operation. A drive motor (not shown) drives at least one of the supply roller 20 and the take-up roller 23 to sequentially advance the polishing pad 40 across the top panel 16. As such, clean preoperative sections of the polishing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing the substrate assembly 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate assembly 12 during planarization. The carrier assembly 30 generally has a carrier head 31 with a plurality of vacuum holes 32 to pick up and release the substrate assembly 12 at appropriate stages of the planarizing cycle. A plurality of nozzles 41 attached to the carrier head 31 dispense a planarizing solution 42 onto a planarizing surface 43 of the polishing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that translates along the gantry 34. The drive assembly 35 generally has actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the carrier head 31 via another shaft 39 such that the drive assembly 35 orbits the carrier head 31 about an axis B-B offset from a center point C-C of the substrate assembly 12.
The polishing pad 40 and the planarizing solution 42 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate assembly 12. The web-format planarizing machine 10 typically uses a fixed-abrasive polishing pad having a plurality of abrasive particles fixedly bonded to a suspension material. The planarizing solutions 42 used with fixed-abrasive pads are generally xe2x80x9cclean solutionsxe2x80x9d without abrasive particles because the abrasive particles in conventional abrasive CMP slurries may ruin the abrasive surface of fixed-abrasive pads. In other applications, the polishing pad 40 may be a nonabrasive pad composed of a polymeric material (e.g., polyurethane), a resin, or other suitable materials without abrasive particles. The plananizing solutions 42 used with nonabrasive polishing pads are typically xe2x80x9cabrasivexe2x80x9d CMP slurries with abrasive particles.
To planarize the substrate assembly 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate assembly 12 against the planarizing surface 43 of the polishing pad 40 in the presence of the planarizing solution 42. The drive assembly 35 then orbits the carrier head 31 about the offset axis B-B to translate the substrate assembly 12 across the planarizing surface 43. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate assembly 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly 12 to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other components, many substrate assemblies develop large xe2x80x9cstep heightsxe2x80x9d that create a xe2x80x9ctopographicalxe2x80x9d surface across the substrate assembly 12. For the purposes of the present application, a xe2x80x9ctopographicalxe2x80x9d surface is a non-planar surface having high and low regions. To enable the fabrication of integrated circuits with high densities of components, it is necessary to produce a highly planar surface at several stages of processing the substrate assembly 12 because even slightly topographical surfaces significantly increase the difficulty of forming submicron features. For example, it is difficult to accurately focus photo-patterns to within tolerances of 0.1 xcexcm on topographical surfaces because submicron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface.
In the competitive semiconductor industry, it is also highly desirable to produce such a uniformly planar surface at a desired endpoint on a substrate assembly. For example, when a conductive layer on the substrate assembly 12 is under-planarized in the formation of contacts or interconnects, many of these components may not be electrically isolated from one another because undesirable portions of the conductive layer may remain on the substrate assembly 12. Additionally, when a substrate assembly 12 is over-planarized, components below the desired endpoint may be damaged or completely destroyed. Thus, to provide a high yield of operable microelectronic devices, CMP processing should remove material until the desired endpoint is reached.
To accurately create highly planar substrate surfaces at the desired endpoint, many CMP applications should initially remove material from high regions on topographical surfaces faster than low regions to change the topographical surface to a planar xe2x80x9cblanketxe2x80x9d surface. After creating a blanket surface on the substrate assembly, CMP applications should remove material from the blanket surface as quickly as possible without adversely affecting its planarity. The CMP processes should then stop removing material at the desired endpoint on the substrate assembly.
One problem with existing CMP techniques, however, is that it is difficult to selectively remove material from high regions on topographical surfaces without also removing significant amounts of material from low regions. It is also difficult to quickly remove material from a blanket substrate surface. For example, many existing CMP techniques that can selectively remove material from high regions on a topographical substrate surface are limited because they have very low polishing rates of the blanket surface. Such topographically selective CMP techniques are thus ineffective at expediently removing material from the blanket surface. Conversely, existing CMP techniques that have high polishing rates of blanket surfaces do not remove high regions on topographical surfaces without also removing material from low regions. Thus, existing CMP techniques generally do not provide both highly selective planarization of high regions on topographical surfaces and fast removal of material from blanket surfaces.
Another problem of CMP processing is that it is difficult to accurately stop planarization at the desired endpoint. One technique for accurately endpointing CMP processing is stop-on-feature (xe2x80x9cSOFxe2x80x9d) planarization in which a hard polish-stop layer of material having a relatively low polishing rate is formed on the substrate assembly so that the polish-stop layer has high points at the desired endpoint of the planarizing process. A softer cover layer of material having a higher polishing rate is then deposited over the polish-stop layer. The polish-stop layer resists planarization at the desired endpoint because the cover layer planarizes faster than exposed high points of the polish-stop layer. Even SOF planarizing techniques, however, may not accurately endpoint CMP processing because the difference in polishing rates between the cover layer and the polish-stop layer may cause xe2x80x9cdishingxe2x80x9d in the cover layer at contacts, damascene lines, shallow-trench-isolation structures, and other areas one the substrate surface where the cover layer dips below the exposed surfaces of the polish-stop layer. Thus, another problem of CMP processing is accurately stopping planarization at the desired endpoint.
The present invention is directed toward planarizing solutions, planarizing machines and methods for planarizing microelectronic-device substrate assemblies using mechanical and/or chemical-mechanical planarizing processes. In one aspect of the invention, a microelectronic-device substrate assembly is planarized by abrading material from the substrate assembly using a plurality of first abrasive particles and removing material from the substrate assembly using a plurality second abrasive particles. The first abrasive particles have a first planarizing attribute, and the second abrasive particles have a second planarizing attribute. The first and second planarizing attributes are different from one another to preferably selectively remove topographical features from the substrate assembly and/or selectively remove different types of material at the substrate surface.
In one particular application of a method in accordance with the invention, the first and second abrasive particles are mixed together in a single slurry including a liquid mixture, a plurality of the first abrasive particles, and a plurality of the second abrasive particles. The single slurry is then deposited onto a polishing pad to provide an abrasive medium having both the first and second abrasive particles. Thus, during a planarizing cycle in accordance with this embodiment, the first abrasive particles abrade material from the substrate assembly at the same time that the second abrasive particles remove material from the substrate assembly.
In an alternative method in accordance with the invention, the first abrasive particles are suspended in a first planarizing solution that is deposited onto the polishing pad during the first stage of the planarizing cycle, and the second abrasive particles are suspended in a separate second planarizing solution that is deposited onto the polishing pad during a second stage of the planarizing cycle. The first and second stages of the planarizing cycle are preferably separate, distinct periods of the planarizing cycle. During the first stage of the planarizing cycle, the first solution is preferably deposited on the polishing pad to selectively remove high regions from a topographical substrate surface. During the second stage of the planarizing cycle, which occurs after the substrate surface becomes planar, the first solution is preferably removed from the polishing pad and the second solution is deposited onto the polishing pad to quickly remove material from the planar surface.
In still another aspect of the invention, the first and second planarizing attributes of the first and second abrasive particles can be the particle size and/or the composition of the abrasive particles. For example, the first abrasive particles can have a first particle size distribution with a first mode and the second abrasive particles can have a second particle size distribution with a second mode. The first and second particle size distributions are preferably selected so that the first abrasive particles selectively planarize high regions on topographical substrate surfaces and the second abrasive particles quickly planarize blanket substrate surfaces. Alternatively, the first abrasive particles can be composed of a first material and the second abrasive particles can be composed of a second material. The first and second materials are preferably selected so that the first abrasive particles aggressively planarize a first type of material on the substrate assembly and the second abrasive particles planarize a second type of material on the substrate assembly either more or less aggressively than the first type of material. The first abrasive particles can also have a first particle size distribution with a first mode and be composed of a first material, and the second abrasive particles can also have a second particle size distribution with a second mode and be composed of a second material.